Such controllable inductors may through the main winding thereof be connected to any electrical circuit, such as a power line, to provide the circuit with an inductance, for example for extinguishing higher harmonic currents generated in the circuit. The magnetic permeability of the core and thus the inductance of the inductor may then be controlled by changing the electric control current brought to flow axially through the core in the control winding. By connecting such a controllable inductor in series to a capacitor a so called harmonic filter may be obtained, which is already known through Applicants' for example, WO 94/11891 of the applicant, and in which the impedance may be controlled to be low for certain frequencies by controlling the inductance of the inductor for eliminating higher harmonic currents having a frequency being a multiple, for example 11, of the fundamental frequency of the network.
Another conceivable field of use for a controllable inductor of this type, in the case that such may deliver an inductance being sufficiently high, is the switching in thereof into alternating current power lines, having a high capacitance stored therein, for example cable networks. By an intercoupling of such an inductor an inductance of a desired size may then be connected thereto and the reactance of the power line may thus be reduced for a more efficient energy transfer through the line.
These controllable inductors have of course only a useful influence upon an alternating voltage, but it is not completely necessary that the main winding is connected to an alternating voltage. For example, it could also be connected to a direct voltage with an alternating voltage superimposed. A disadvantage of such controllable inductors already known is the fact that the alternating voltage in the main winding induces an alternating voltage in the control winding having a frequency being twice the fundamental frequency in the main winding. This voltage gives rise to harmonic currents in the network and causes losses in the core.